New findings on the blowfly labellar taste response of Protophormia terraenovae

An electrophysiological investigation was performed to analyse activity recorded in response to stimulation with concentrated and diluted solutions of NaCl, sucrose, formamidine acetate, and sodium acetate from labellar chemosensilla of the dipteran Protophormia terraenovae. A computerized analysis of this activity led to the finding of four kinds of spikes (A, B, C, and D) which differed in their wave forms. The forms of spikes A, B, and C are described in the literature as being evoked by activation of the specific salt, water, and sugar neurones respectively. The fourth type of spike (D) recorded in response to formamidine acetate and sodium acetate is probably generated by a fourth chemosensorial cell that has not yet been defined functionally. These two acetates evoke activities that are equivalent both in spike frequency and time distribution even at low concentrations. The results suggest that the acetate ion in the blowfly effectively stimulates the fourth chemosensory neuron present in the sensillum. The activation appears to be involved in signalling acidity to the insect.